POS0567 COMPARISON OF SURVIVAL ON TREATMENT AMONG NEW USERS OF BIOSIMILAR VS. ORIGINATOR BIOLOGICS IN INFLAMMATORY ARTHRITIS: POPULATION-BASED EVIDENCE FROM A NATURAL EXPERIMENT DUE TO A POLICY CHANGE
Authors: D. Lacaille, J. A. Aviña-Zubieta, Y. Zheng, N. Lu, H. Xie
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> British Columbia (BC) health policy mandated the use of biosimilars, when available, for all new anti-TNF prescriptions after June 2017. <h3>Objectives</h3> To compare drug survival (surrogate marker of effectiveness and safety) after initiation of etanercept and infliximab for inflammatory arthritis in new users of biosimilars vs. originators, using historical controls pre-policy change. <h3>Methods</h3> Using administrative health data, we identified all incident users of a new anti-TNF with rheumatoid arthritis (RA), psoriasis or psoriatic arthritis (Pso/PsA), or ankylosing spondylitis (AS). The biosimilar cohort started etanercept or infliximab between 07/01/2017 and 12/31/2019, were followed until 12/31/2020 (post-policy period). Historical controls started etanercept/infliximab originators between 01/01/2014 and 06/30/2016, were followed until 06/30/2017 (pre-policy period). To control for potential temporal trends, new users of adalimumab (no biosimilar available then) served as comparators. Discontinuation was defined as no prescription renewal for ≥6 mos. Individuals were followed from anti-TNF initiation until discontinuation or censoring due to death, moving out-of-province, or follow-up end, whichever occurred first. We applied weighted Cox Proportional Hazard Models that handle non-proportional hazards combined with propensity overlap weighting to estimate the adjusted hazard ratio (aHR) of discontinuing anti-TNFs, in people who started a biosimilar vs. the respective originator, after controlling for potential confounders. To control for temporal trend, we employed the difference-in-difference (DID) method, comparing drug survival among new biosimilar vs. originator etanercept/infliximab users with adalimumab users post- vs. pre-policy change, computed as the difference between the logarithms of aHRs for etanercept/infliximab and for adalimumab. We report the exponential of DID estimates (i.e. the ratio of the two aHRs). <h3>Results</h3> Our sample included 827 biosimilar etanercept users (RA:576, AS:171, Pso/PsA:80) and 271 infliximab users (RA:150, AS:54, Pso/PsA:67); 1312 etanercept and 230 infliximab originator users; and 2213 adalimumab originator users post- and 1773 pre-policy change. Discontinuation rates per 100 PY are shown in Table 1A. After adjusting for baseline covariates (Table 1B), and accounting for temporal trends (Table 1C), the risk of discontinuation was similar for biosimilar vs. originator etanercept and infliximab users. <h3>Conclusion</h3> Real-world population-based data in BC shows that incident users of biosimilar etanercept and infliximab for inflammatory arthritis have comparable duration of treatment to users of originators. <h3>Acknowledgements</h3> This research received funding from the Canadian Initiative for Outcomes in Rheumatology cAre (CIORA) via the Canadian Rheumatology Association. Dr. Lacaille is supported by the Mary Pack Chair in Arthritis Research from the University of British Columbia and The Arthritis Society of Canada. Dr. Antonio Avina Zubieta is a BC Lupus Society Research Scholar and a Walter &amp; Marilyn Booth Research Scholar. Dr. Hui Xie is supported by the Milan Ilich/ Merck Chair in Statistics for Arthritis and Musculoskeletal Diseases from Simon Fraser University. <h3>Disclosure of Interests</h3> None Declared.